Budgeting for GrGlTextureRenderTarget isn't correct

Issue description

GrGlTextureRenderTarget derives from both GrGLTexture and GrGLRenderTarget, so we have one flag (GrGpuResource::fFlags) to determine if the resource is wrapped. GrGlTextureRenderTarget can have an unwrapped render object, and a wrapped texture, and when that happens the resource will report itself wrapped, and as a result, will not use FBOs from GrGLRenderTarget during budgeting.
GrGpuResource::setContentKey, GrGpuResource::setScratchKey and GrGpuResource::setBudgeted may not work correctly.